That font is used for creating text on graphs.
There's a translated readme.txt in that folder too. May be the translator has given some guidelinges... Check it out (I can't -> don't speak russian)
no, there are no guideline.
in graphlib.php i seen using optional lang_decode.php, may be it can help. As sample mey be used \lang\el\fonts\lang_decode.php
Other way - check installed or not "iconv" functionality at our server.
I can't check it now. When i check it, i'll writing results here.